This invention relates to poly(arylene sulfide). In one of its aspects this invention relates to phenylene sulfide polymers. In another of its aspects this invention relates to heat treatment of arylene sulfide polymers. In another of its aspects this invention relates to extrusion of arylene sulfide polymers. In still another aspect of this invention it relates to stabilization of melt crystallization temperature of arylene sulfide polymers.
Melt crystallization temperature (Tmc) is an important characteristic in the determination of final use of poly(arylene sulfide), particularly poly(phenylene sulfide). The melt crystallization temperature (Tmc) indicates the point at which the polymer becomes crystalline. Tmc is an important characteristic of poly(phenylene sulfide) that is to be used in fiber and film making, e.g., the lower the Tmc of the polymer: the thicker film that can be formed from the polymer.
It is well known that subjecting poly(phenylene sulfide) to treatment requiring elevation of temperature can cause an increase in the melt crystallization temperature. It has now been further determined that for PPS there seems to be a critical range of temperature between 260.degree. and 320.degree. C. within which the slow heating process usually used in elevating the temperature of the polymer is particularly detrimental in increasing the Tmc.
The process of the present invention sets forth a method by which the increase in Tmc that often appears in poly(phenylene sulfide) treated by elevating the temperature of the polymer through a temperature range of up to about 320.degree. C. can be at least alleviated if not completely overcome.
It is therefore an object of this invention to provide a method for minimizing the increase of Tmc in poly(phenylene sulfide) subjected to heat treatment in a range of temperature up to about 320.degree. C. It is still another object of this invention to provide specific temperature treatments for an extrusion process in which the temperature of the polymer is raised through a temperature range between about 240.degree. C. and about 320.degree. C. It is still another object of this invention to produce heat treated poly(phenylene sulfide) without adversely raising the Tmc of the polymer. It is still another object of this invention to subject poly(phenylene sulfide) to an extrusion without raising the Tmc of the polymer.
Other aspects, objects and the various advantages of this invention will become apparent upon reading the specification and the appended claims.